Sacral neuromodulation with ultra-low stimulation intensity is effective in faecal incontinence – results from a randomised study with a one-stage implant procedure

Introduction: In sacral neuromodulation (SNM), the stimulation intensity is set at the sensory threshold (ST) level. However, subsensory stimulation as low as 50% of ST has proven effective in reducing faecal incontinence episodes. Aim: To explore the relationship between functional outcomes and varying subsensory stimulation amplitude in newly implanted patients. Method: This randomised, double-blind study was designed to include patients with ≥ 1 faecal incontinence episodes/week despite maximal conservative therapy. As part of another trial, patients were offered a one-stage procedure. Postoperatively, patients were randomised into two groups. G-1 received stimulation at 0.05 V, at 50% and 90% of the ST in three 4-week periods, followed by 12 weeks of stimulation at the ST. G-2 received stimulation at 90% of the ST in three 4-week periods, followed by 12 weeks of stimulation at ST. Patients were evaluated after each period using St. Marks’s Incontinence Score and a visual analogue scale (VAS) for patient satisfaction regarding social function, bowel function and quality-of-life, along with a bowel habit diary. Results: In total, 73 patients with a median age of 60 years [interquartile range (IQR: 50–69 years)] completed the trial. Faecal incontinence episodes were significantly reduced at all follow-ups, with no differences between groups. The only statistical difference between groups was deltaVAS for bowel function after 4 weeks. In G-1 with ultra-low stimulation amplitude [0.05 V – equivalent to 9.6% (IQR: 6.5–13.4) of ST], the improvement compared with baseline was 30 points (IQR: 10–50) significantly lower than G-2 with an improvement of 50 points (IQR: 10–70) (p-value: 0.05). Conclusions: Subsensory stimulation is feasible in newly implanted patients with faecal incontinence. An amplitude of 0.05 V is as effective on the functional outcomes as stimulation with higher amplitudes.